Abstract: A liquid flow meter (50), including a microcontroller (60) and associated algorithm, monitors urine flow through a cartridge trap (20). Measuring the duration of such flow and the number of times the urinal is used will determine, in accordance with preset criteria, when servicing or replacement is needed, and alerts a service person to that effect by a warning light (68) or other signal. Because urine has a high mineral content, it is electrically conductive, effective to complete circuits between closely spaced metal contacts (62a-62c, 64a-64c) coupled to the PROM, which allows the manner and existence of the urine to be detected. The liquid flow meter is installed in the cartridge trap by utilizing and placing a split ball stem (52) located at the base of the meter into a mounting hole (42) located in the center of the drain holes (36) on the cartridge cover (26).